No.4 bolt problem

[ShaveTail]

I just bought a 1916 BSA to work on (don't have it yet, more later!) and this prompted me to finally go back to the bolt problem on my No.4 mk 1 Longbranch.

The bolt tends to jump the track, that is the bolt head pops up out of the takedown notch about one time in three when the bolt is worked. To tighten it completely would bring it to about 11:00...normal? Think the problem is with the bolt, or the receiver rail?

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[Brian Dick]

It's most likely the receiver rail. They can chip or wear on Mk.1* rifles which causes the problem. Some weld them up and recut with a good sharp file.

[Alan de Enfield]

The bolt tends to jump the track, that is the bolt head pops up out of the takedown notch about one time in three when the bolt is worked. To tighten it completely would bring it to about 11:00...normal? Think the problem is with the bolt, or the receiver rail?

No quite sure what you are sayng here.
Are you saying that the bolt head when tightened up into the bolt body is at 11 O'clock and is this when viewed from the rear or the front ?

This is called bolt-head overturn and is 'bad'. Maximum overturn should be 10 degrees (later increased to 15 degrees)

[Beerhunter]

The bolt tends to jump the track, that is the bolt head pops up out of the takedown notch about one time in three when the bolt is worked.

It was a relatively common problem with Mk.1*s at school. It was caused by a chipped rail. Rifles to which it occurred were condemned.

[Son]

I'll go down a different track here.... The bolt head should just go straight back as the bolt is withdrawn. For the head to rotate up out of the slot it must have torque applied to it. The only place this can come from is the striker spring. When you lift the bolt handle, the bolt body rotates, but the striker stays still. The striker spring may be spragging (technical term for digging in) the surfaces the ends of it contact at the back of the bolt body and the collar on the striker. When the bolt is withdrawn, the stored torque in the spring rotates the bolthead into the gap in the rail as soon as it gets there.

If you don't want to strip the bolt down, just try giving it a good flush out (bolthead off) with a pressure pack cleaner and then liberally apply some good oil.
If you do strip it, dress the ends of the spring on an oilstone. Check the back of the striker collar for any tiny burrs. The inside back of the bolt body is a bit trickier...

[Peter Laidler]

Good advice re the striker spring there Son. We had a repair programme for repairing torm bolt head guides. We'd wait for about 20 to come through and then we'd do the lot in one hit. I detailed the repair here a while ago

[ShaveTail]

Thanks for the replies guys. It wouldn't surprise me at all if this rifle has a chipped rail (this bugger has been a bastard all around from day one) but 'sprannging' rings a bell for another reason. I've noticed before that once cocked and engaged, if the bolt handle is nudged at all it will literally shoot the bolt back. Surprised the hell out of me the first time it happened and doesn't really seem like a normal thing, come to think of it.

I think I better detail strip the bolt again right now. This rifle was so packed in a combo of rust, mud, and dried cosmo when received that it took two weeks of solid cleaning just to find out what was underneath, so I had to tear down the bolt to clean it...even though I wasn't that versed on the Enfield. I'd hate to scrap her because 1.) she is all matching, even the stocks, and 2.) caused me to get a tetanus shot when I stabbed myself in the thumb reseating the trigger spring whilst covered to the elbows in grime. My blood is quite literally in this rifle.

[Bruce_in_Oz]

The problem with the 1* "relaxation" is that it assumes that the bolt and body are both in spec all the time.

As we are dealing with "vintage" equipment that often has not been near a real workshop for inspection for fifty years, there is wide scope for things to "flog out" as we say in Oz.

The main support for the bolt is in the split bridge behind the locking recesses and the laughably small remnant of the bolt way in the left wall of the receiver/body. If you withdraw the bolt about hlaf-way and wiggle it up and down you can always detect movement.

If the body of the bolt can float up and down during operation, there is a good chance that the small rib on the bolt head will start to contact the flat surfaces on the ends of the cut-out in the rib on the body.

There is a sort-of solution and this is where I need a bit of technical history advice.

The way to prevent "floating" bolt heads tearing chunks off the receiver rib is to slightly bevel the front and rear top corners of the small guide rib on the bolt head.

This is not an original idea, as examonation of numerous No4 bolt heads over the years turns up quite a few. Some of the bolt heads with this feature have been new and unused, others show signs of extensive service. Many are Canadian, but UK manufactured specimens have been seen.

To my mind, it would have been the height of optimism to expect this sort of damage not to occur on the Mk1* arrangement.

I have never seen a reference in the limited amount of UK and Canadian documents that I have. Is this tiny feature an officially mandated thing or something done by the "brotherhood of the eagle eye"?

[Bruce_in_Oz]

But wait, there's more! Sent the last lot too early::

The mention of bolt head "overturn" is also very important.

If the bolt body is a bit loose in the receiver AND the bolt head can be rotated past the long (RH) lug on the bolt body, the things will be even worse.

An additional issue is whether the action is being cycled with or without cartridges in the magazine. The relatively light magazine spring force behind a stack of cartridges adds a bit of upward pressure on the bolt. This may provide some counteraction to the downward torque applied when the bolt is driven forward. Note that because the bolt knob is some distance from the axis of the bolt, there MUST be some force applied in a non-axial direction. As the bolt knob is ABOVE the axis of the bolt, on the rearward stroke, the front of the bolt will be forced upwards; on the forward stroke the bolt head will be forced downwards. As the front of the bolt "dives" the bolt head will rotate about the line of contact on the RHS cartridge guide. Thus the guide rib on the bolt head will be trying to move upwards; not a good thing with a 1* body. Any vertical rocking of the bolt body is also translated into vertical wear at the quite small front and rear bearing surfaces behind the locking shoulders.

The looser the bolt, the greater the rocking and the faster the wear. Sloppy bolt fit + worn receiver + loose bolt head = Bad News in a 1* rifle.